Despite photovoltaics (PV) being one the fastest-growing energy technologies, the sharp decline of price levels in the worldwide solar module market has forced manufacturers to re-engineer production processes and streamline their operations to stay competitive. The most promising of the thin-film PVmaterials in the industry is CIGS (Copper Indium Gallium Selenide), which has demonstrated lab efficiencies on par with traditional crystalline silicon technologies while having the potential to substantially reduce costs.
CIGS has also shown potential for higher energy yield response to cloudy and diffuse light circumstances. In the lab, CIGS has achieved performance levels of 20.1 percent efficiency, as reported by ZSW* of Stuttgart and verified by Fraunhofer ISE*.
Thin-film PV manufacturers today require highly-automated systems to arrive at the cost efficiencies needed to compete on the world market. Thin-film PV manufacturing processes must provide continuous high-speed throughput while maintaining zero defect rates, and be capable of shifting production volumes quickly with minimal set-up times. One such manufacturer of CIGS modules that has streamlined its manufacturing process and successfully weathered the market shift is HelioVolt Corporation, based in Austin, Texas.
HelioVolt has developed a proprietary advanced manufacturing process FASST reactive transfer processing for producing monolithically-integrated thin-film modules which have enabled it to become a prominent player in the production of practical and economical solar panels aimed at the fast-growing commercial rooftop and ground-mount solar application markets. Unique CIGS Manufacturing Process HelioVolts CIGS FASST process is a two-stage reactive transfer process that separates chemical deposition from synthesis. The process relies on chemical reaction between two separate films to form CIGS.
These films are brought into close distance and rapidly reacted under pressure in the presence of an electrostatic field while heat is applied. The use of two independent thin films provides the benefits of independent composition and flexible deposition technique optimization, and eliminates pre-reaction prior to the synthesis of CIGS. The separation of the deposition process from the synthesis step provides the unique ability to control the key parameters required for superior material performance, resulting in the efficient absorption of a broad band of the solar spectrum.
The process uses a fraction of the expensive semiconductor material utilized in silicon modules. The monolithically-interconnected modules mean no cost-cutting, testing, binning or stringing of cells. The modules are true PV integrated circuits (PVICs). Initially developing small-cell, 6-inch PV wafers in 2007, the company now manufactures 1.2m x 0.6m (4.0 feet x 2.0 feet) full-size CIGS modules with a rating up to 85 watts per panel.
HelioVolts modules have excelled at extensive accelerated environmental testing, and have been certified by Intertek* to UL 1703 and IEC 61646 and IEC 61730 standards. HelioVolts Plant Equipped with Material Handling Systems Designed for Streamlined Movement of CIGS Panels To facilitate the production of its high-quality monolithically-interconnected CIGS, in 2008 HelioVolt opened a new 125,000 square-foot, 20 megawatt capacity production plant in Austin, Texas. Through every step of the process from receipt of incoming flat glass to the two stages of CIGS semiconductor deposition, to the assembly of the final modules and testing, and finally packaging for shipment the plant is a showpiece for streamlined CIGS manufacturing and throughput.
Transporting the CIGS panels to the production processes throughout the plant, and providing precision infeed and take-away of the glass panels for these systems required an integrated flow of material handling systems to accomplish seamless throughput. To design and implement this material handling system, HelioVolt brought in Shuttleworth, Inc. Shuttleworth, powered by Pro Mach, Inc., has a long history of providing material handling systems, such as conveyors, accumulators and buffers for transporting flat glass, and solar panels, as well as for the transportation of many other electronic components and assemblies.
The company leads the solar industry with providing specialty conveyor systems applicable to ISO Class 6 and for clean environments to ISO Class 3. The factory line was designed in collaboration with a number of partners, including Shuttleworth, says John Prater, Vice President of Business Operations with HelioVolt. Shuttleworth was a valued partner in creating the line design and the automation schemes that have enabled us to demonstrate scalability and achieve the performance results like we have seen. From the initial receipt of the flat glass into our plant, it is loaded onto the automated conveyor system, continues Prater. As the glass goes though each of our processing steps, through to the end of the line, the conveyors are transporting the glass panels. Our facility has every automated application that Shuttleworth produces for the solar industry.
More than 1,000 linear feet of automated conveyor systems were custom-designed and installed into the HelioVolt plant to interface with the facilitys robots and automated production equipment. A multitude of custom devices and mechanisms were incorporated throughout the system to stop, buffer, transfer, rotate, and raise and lower the 4-foot x 2-foot panels. The conveying system utilizes an open roller and roller-shaft surface design that was incorporated throughout the facility. This allows devices to easily be positioned from underneath, making for a very clean design and the ability to move the CIGS panels without interference.
Product stops, product positioning clamps and photo eye sensors were all mounted below the roller surface and came up underneath the rollers to access the panels. Lift-and-rotate (LAR) devices are used to change the orientation of the panels on the conveyors. The LAR devices rest just below the roller surfaces until activated. The CIGS panel is conveyed to a product stop, which positions it over the LAR device. The LAR, activated by a sensor, then lifts the panel above the roller surface before rotating it to the desired orientation. The LAR device then lowers the CIGS panel to the conveyor surface where it is conveyed in its new orientation.
Lift-and-transfer (LAT) devices installed in the material handling system are used to provide a smooth and accurate CIGS panel transfer at a 90-degree angle to the original transport direction. The LAT mechanism is mounted within the conveyor frame and consists of two or more mini-belt conveyors that reside below the roller surface when deactivated. Upon activation, the LAT device lifts the product above the conveyor surface and transports it 90-degrees in either direction to a predetermined point. Lift-and-transfer devices can transport panels very precisely to multiple conveyor lanes based on HelioVolts panel/order identification tracking system.
HelioVolts conveying system is also equipped with Slip-Torque technology which provides low line pressure throughout the continuous-motion accumulation conveyors. This allows for precise product placement and virtually eliminates CIGS panel damage by creating low back pressure. Should the line need to slow or stop, the conveyors can continue to take panels from the upstream line for a specified period of time instead of stopping the line. A low-pressure accumulation buffer absorbs irregularities in the production flow, and provides a smooth, even flow on the line. Slip-Torque utilizes individually-powered rotating roller shafts and loose-fit rollers, which become the conveyor surface, powered by a continuous chain to control the drive force. The size and weight of the panels determine the driving force and roller selection. When the CIGS panels stop on the surface of the conveyor, the segmented rollers beneath the cells also stop.
A critical factor in the selection of the material handling system was based on total cost of ownership, Prater says. The Shuttleworth system represents an excellent long-term process solution to the production throughput challenges encountered in our plant.
